The present invention relates in general to gas mask design, and in particular to a new and useful design for the periphery of the gas mask which makes an efficient seal with the face of a wearer while avoiding discrete pressure areas which lead to discomfort.
The periphery or face seal of a full-face respirator or protective mask, plays a critical role in determining the effectiveness of the respiratory protection system. The periphery of a full-face respirator is that portion of the mask facepiece which contacts the wearer's skin, forming a leak-proof seal which isolates the interior of the mask, the wearer's eyes and the wearer's respiratory tract, from a contaminated environment. Breathing air is filtered through a chemically absorptive medium, such as activated carbon, to remove toxic materials. If the face seal is ineffective or inefficient, contaminated air can leak past the periphery, mix with the filtered air, and be inspirated, thus exposing the wearer to the hazard he or she is attempting to avoid.
The currently fielded, standard military respiratory protective masks (M9A1 Special Purpose, M17 series CB Protective masks, M24 Aviator's mask, and the M25A1 Tanker's mask) have a flat-type periphery shown in FIG. 1. The flat periphery is a very common, effective periphery design for most respirator uses, but it has limits to its effectiveness.
A more effective design for a face seal is the so-called inturn periphery. During work on extra-small (XS) M17 series masks, a bubble inturn was developed to enhance the protection of the mask (FIG. 2). The bubble inturn periphery has superior face-sealing characteristics, due to its ability to conform to facial features more readily, and its larger sealing surface. The inturn periphery as designed, however, had a serious problem with a painful pressure point (hot spot) along the centerline of the periphery, mostly at the forehead of the mask, due to the thickness of the periphery at that point. To alleviate the problem with the hot spot, the XS M17 mask returned to a flat periphery along the forehead. This eliminated the hot spot, but also reduced the effectiveness of the face seal.
During the development of a series of masks designated XM29/30, a new periphery was designed and patented by John Scavnicky and Malcolm Little, under U.S. Pat. No. 4,595,003 (which is incorporated here by reference). A flat inturn periphery as shown in FIG. 3 was used across the forehead, and a revised bubble inturn as shown in FIG. 4 was used along the cheeks of the mask. The two were blended together at the temple of the mask. This mixture of peripheries has proven to be very comfortable, and was another improvement in protection over the standard flat periphery. This is the design of the periphery which has been carried forward into a protective mask program designated the XM40.